1. Field of the Invention
The invention relates to a burner device comprising a burner chamber filled at least partially by a porous body, an evaporation zone upstream of the burner chamber for evaporating liquid fuel supplied via a fuel inlet line, an igniter for igniting a combustion mixture of evaporated liquid fuel and combustion air supplied via a combustion air inlet line to the evaporation zone as well as an exhaust discharge downstream of the combustion chamber.
2. Description of Related Art
One such burner device, also termed a porous burner, is known from German Patent Application DE 101 60 837 A1. Typical of a porous burner is its porous body, i.e., a body of porous material which at least partially fills the burner chamber. The porous material of such a porous body is especially a non-oxidizing material, such as SiC, SiN, or also high-temperature oxides, such as, for example, Al2O3 or ZrO2. Porous bodies are often employed to improve the emission quality of a burner device. Since a defined combustion over a large surface area is involved in the porous body, making use of a porous body achieves a stable total combustion so that the burner can work at lower temperatures which, in turn, reduces the Nox concentration in the exhaust gas. In addition, portions of the porous body, as disclosed for instance in the aforementioned patent application, are used as a flame trap to prevent flashback to the inlet lines or into the evaporation zone. This is achieved in that a very small pore size is provided in the portion of the porous body facing the inlet line or evaporation zone so that no flame can form there. Adjoining this small pore zone, larger pores are provided in the porous body which make for a stable flame formation, as a result of which the aforementioned objects of a stabilized flame formation and the flame trap are achieved. However, the small pore zone of the porous body results in a considerable pressure loss. This is why, despite the flame trap, flashback may occur especially in the stationary operating points of the burner which results in higher exhaust emissions or even the burner, or parts thereof, being ruined as a result.
Also known are porous burners for the combustion of gaseous fuels or fuel gases. Indeed, most porous burners are designed as gas burners. One example of such a gas porous burner is disclosed in German Patent Application DE 199 60 093 A1. This gas porous burner comprises a pot-type porous body, the interior of the pot serving as the mixing zone into which a combustible gas is introduced via a fuel gas inlet line and is mixed with combustion air, likewise introduced into the interior of the pot. The outer portion of the pot interior also serves as a reaction zone, i.e., combustion zone, the thickness of which can be controlled by the flow and pressure of the inlet gases. Stabilizing the flame materializing in the reaction zone is done in the porous body. Such a device is very sensitive to flashback, and thus, the fuel gas inlet line of the burner needs to comprise corresponding protective devices.
Porous burners for liquid fuels, on the one hand, and porous burners for fuel gases, on the other, feature completely different structures as are typically illustrated in the aforementioned patents.